The present invention relates to improvements in handbrake operating linkages for use on railroad cars, and particularly to such linkages for a multi-unit articulated railway car.
Safety regulations applicable to railroad cars require the ability to apply brakes manually to at least half of the axles of each car, with ample braking effect. Preferably, application or release of the brakes of all of the manually braked wheels should be possible from a single operator position such as a hand wheel or equivalent mechanism located at one end of a car. It should be possible for brakes to be applied manually in a short time, but it must also be possible for a single person to apply force manually to the brake shoes to grip all the affected wheels with sufficient braking effect. Further, because railroad cars on which such braking systems are installed are intended to carry a maximum load of stacked rectangular cargo containers, only a limited amount of space is available to locate the brake operating linkages, typically along one side of each car unit.
In a multi-unit articulated freight car the several units, and their wheeled trucks, all pivot with respect to one another as the car negotiates uneveness or curves in the track. A certain amount of slack and freedom of movement must be provided in the manual brake operating mechanisms and linkages, then, to prevent application of the brake shoes from occurring purely as an unwanted result of the relative movement between the trucks and units of the multi-unit car. The amount of such slackness and freedom of movement of the brake applying linkages should be kept as small as possible, in order to minimize the time and effort necessary to take up such slack preliminary to bringing the brake shoes forcefully into braking contact with the surfaces of the wheels on which they must press to create a braking force.
Because of the length of multi-unit articulated cars, which is considerably greater than the length of non-articulated cars, and because of the need for some linkages spanning the spaces between car units to be offset from either the center line or pivot axis of the articulating couplings between car units, a certain amount of slack must be provided to allow for negotiation of curves in a railroad track without causing undesired application of brakes. Slack must be provided as necessary at each truck when the manually-operable braking system is released.
The necessarily provided slack in such a manually-operable braking system needs to be taken up quickly during manual application of the brakes, but the same handbrake operating mechanism must, nevertheless, be capable of applying the brake shoes with ample force once the slack has been taken up, even though application of a large force by means of a linkage providing a mechanical advantage would appear to be at odds with the desired rapid take-up of slack.
Previously, numerous manually operable railroad car handbrake systems have provided allowances for relative movement between railroad car bodies and the trucks on which they are supported. Among these, most notable is the brake system disclosed in Morrison et al. U.S. Pat. No. 4,346,790, which discloses an arrangement for manual operation of brakes on an articulated multi-unit freight car, in which brake rods span the gaps between adjacent units of the car.
While the Morrison et al. patent discloses a brake system for articulated multi-unit cars, it makes no provision for rapid take up of the necessary amounts of slack in the linkages, with the result that considerable time may be spent taking up such slack before the braking system provides any braking effect. On the other hand, were the hand wheel or equivalent mechanism arranged to take up slack rapidly, the resultant amount of force which could be applied using the hand wheel might not be sufficient to apply the brake shoes to the wheels to provide sufficient braking effect, since the choice of greater distance moved results in a smaller force moving through that distance, for a given available amount of power, i.e., one brakeman's abilities.
What is needed, then, is an improved mechanical arrangement for manual operation of brakes for an articulated multi-unit rail car, which provides for reliable release of the brakes with a minimum of slack being created thereby, and by which it is possible manually to take up slack rapidly and thereafter to apply the brakes with ample force to the wheels of several trucks of the car from a single location of the car.